CNC tooling

from Applied Science Youtube channel.

TLDR:

...so now we know, to machine this pocket feature (inner shape, like a dish), we're gonna use a high speed steel (HSS) tool, and it's going to be as long as necessary, and the diameter (of the tool) is small enough to make these features (inner radiuses) come out correctly.

start from your tooling.

the most important factor in cnc machining is the tooling. no matter how fast and how big your machine is, it all comes down to the point of contact between:

• your cutting tool
• your cutting material

and it's not even the cutting tool itself, but the very edge where the tool comes into contact with the material being cut.

probably the single most important thing when setting up a machine operation is the total rigidity of your whole setup.

use the shortest tool possible.

because it minimizes wobble. the more wobble, the less rigid (see above). this will cause the cnc piece to have a bad finish.

always use the largest diameter tool possible for the job.

the tool should be a diameter that is the largest possible to cut away material, but should be:

• small enough to make the smallest inner radius,
• outer radiuses essentially don't matter, cause basically all tools can do it
• the best is when you design your inner radius of the cut to match exactly the radius of a cnc tool bit. e.g. 30mm radius drill bit to cut 30mm inner radius shapes.
• small diameter cutters BREAK EASILY.

cnc tooling bit coating is essentially a non-factor in aluminium cnc

when milling soft stuff like aluminium and plastic, the most important thing is to have a sharp tool.

the main cutting parameters in cnc machining

this is essentially what is written in the gcode (the language that the cnc machine reads to do the work)

1. how fast to spin your tool
2. how quickly to push it through the work (the material being milled)
3. how deep it should plunge into the work for every pass

1. how fast (max RPM) - your RPM should not exceed the calculated RPM, calculated from the SFM unit on the tool manufacturer's feed and speeds chart.

this is measured on the feeds and speeds chart, based on the tooling used + material being cut

TODO: calculation here

e.g. HSS tooling used to cut aluminium 6061 --> 40 - 60 sfm

2. how fast to move (target chip load) - your Chip Load should not be lower then (can't be too much higher or lower than calculated)

what determines this:

• cutting type (slot etc)
• tool material and size
• material being cut

for a:

• slot type cut
• on a 3/8' inch tool
• when cutting aluminium

TODO: calculation here

your chip load should be (e.g.) 28.9 inches per minute

Chip Load is a measure used to calculate how much material is removed for every tooth on the cutter (there are 2,3,4 tooth cutters etc)

you'd be surprised how fast you can dull a cutter by not pushing hard enough

3. how deep - generally keep to less than half the depth of your tool bit diameter

good rule of thumb is to NOT plunge more than 1/2 the diameter of the cutter.

e.g. your tool is 10mm diameter, therefore you should plunge less than 5mm

there are usually two rounds to cut, a roughing and finishing cut

roughing cuts are purposefully cut undersized, so that the finishing cut can bring it to the final dimension.

finishing cut will probably only remove about 5 or 10 thousandths of an inch

cooling

aluminium needs cooling. because aluminium flakes will generally stick to the cutter or stick to the work itself and cause the entire piece to be hot (global heating issue)

if you don't have coolant, the only option is to lower the rpm speed, while keeping chip load constant.

the direction to push a cutter if it's not cutting a slot

minute 21:10

terms: climb milling, conventional milling

reducing vibration without reducing chip load

Key terms

• speeds and feeds
  • e.g. speed = 3800rpm, feed = 28.9 inches per minute
• chip load
  • some cnc software can just take the chip load of your
• feed and speeds chart
  • usually provided by the manufacturer of the tool that you have, in order to provide you data about some key metrics that map the relationship between the cutting tool and cutting material.
  • e.g. HSS Feeds and Speeds chart for Non-ferrous metals (like alumnium)
• High speed steel (HSS)
  • a common (cheapest) type of material used to make tooling. Soft, less brittle, more forgiving
• carbide
  • very high end
  • allows for higher speeds, saving time
    • most job shops use it because it saves time, and time is the most important factor to them (not to home cnc makers)
  • very brittle
    • very sensitive to vibration, which will easily chip away the sharp parts of the tooling
• tungsten carbide
  • resistant to heat, so may be a good middle ground tooling material to use for home shops.
• tooling coating
  • aluminium titanium oxide
  • titanium nickel oxide
  • and stuff
  • they're useless when it comes to cutting aluminium.